Hungarians are voting in a referendum that is all but certain to send a strong -- if symbolic -- antimigrant message to the rest of the European Union.

Prime Minister Viktor Orban has been a leading voice against allowing Syrian refugees and other migrants to settle in Europe -- erecting two border fences to keep out illegals -- and he has urged his compatriots to reject an EU quota to accept such outsiders in the vote.

Opinion polls suggest that Hungarians overwhelmingly back him, and they have been warned by senior politicians from Orban's ruling, right-wing Fidesz and other parties of perceived dangers from abroad that include a dilution of Hungarian culture or the risk of extremist attacks.

Stoking such fears, some billboards asked potential voters: "Did you know? Since the start of the migration crisis, the number of harassment cases against women has jumped in Europe."

"We do not agree with the quota, of course, because it would let people coming into the country without any control and although we would try like to help the refugees but still not like this," voter Zsuzsanna Toth told AP in Budapest on October 1. "I mean, it has to be some kind of control to let the people in, so the referendum is really important. Otherwise, it is going to change the culture of the nation."

But the so-called quota referendum is likely to remain symbolic unless voters defy research suggesting less than the required 50 percent of eligible voters will bother to turn up. An hour before the end of voting the figure was about 40 percent.

Ruling party lawmaker Gergely Gulyas said that voter turnout will be around 45 percent based on exit poll data, and that around 95 percent will have rejected the quotas.

Past referendums on NATO membership, in 1997, and EU membership, in 2003, each failed on that count.

But EU officials fear nevertheless that the Hungarian referendum will heap more pressure on them as they grapple with the challenges presented by the ongoing flow to Europe of migrants fleeing conflict and other hardship in the Middle East, Afghanistan, or elsewhere.

After casting his vote in Budapest, Orban said he would go to Brussels next week to start talks, empowered by the outcome of the referendum, "to achieve that we should not be obliged to accept people in Hungary whom we don't want to live with."

He added that his government might modify the Hungarian Constitution after the vote.

Orban authored an opinion piece that appeared on October 1 arguing that people had "a duty" to help him resist the "liberal methods" practiced by the "Brussels elite."

"Mass migration without control means a real threat. It endangers the peaceful and safe European way of life," Orban wrote in the Magyar Idok newspaper. "With the referendum, we can send a message to each European...telling them that it depends on us, European citizens, to bring the EU back to reason, with common effort, or let it disintegrate."

EU interior ministers last year approved a plan to impose mandatory quotas to relocate some 120,000 migrants from front-line Schengen zone states to other countries, although the vote produced sharp and lasting divisions.

But Hungary has rejected the relocation to that country of even a single person under the scheme, and along with neighboring Slovakia has mounted a legal challenge to its legitimacy.

In another sign of tension within the EU over migrants, French police opened fire with tear gas and water cannons on October 1 after violent clashes erupted when pro-migration activists tried to hold a banned demonstration next to a ramshackle migrant camp in Calais dubbed the "Jungle."

At least 10 police officers were injured in the three-hour melee, French authorities said.

The camp houses between 7,000 and 10,000 migrants, many of them intent on getting across the English Channel to the United Kingdom, and has been slated for closure by winter.

Turkish and EU leaders agreed a complex deal in March that Europeans hoped would curb massive migration flows into Europe -- some of it via Turkey -- in exchange for billions in aid to Ankara, fast-track visa conditions, and possible new impetus for EU membership talks.

But Turkey's president, Recep Tayyip Erdogan, on October 1 signaled mounting impatience with Brussels' implementation of that agreement and suggested in the context of Ankara's pursuit of EU membership that "it's their choice to continue the path with or without Turkey. [But] they should not hold us responsible."